Calcium silicate shaped products, generally known as sand lime shaped products, are made from sand, lime and water (e.g., slaked or unslaked lime (quicklime or hydrated lime)). They are typically mixed together, molded under mechanical pressure and may be hardened under steam pressure, such as in an autoclave. Sand lime shaped products may have several different advantages over other masonry products such as (but not limited to) clay and/or concrete pre-cast products. For example, sand lime shaped products may have accurate dimensions, smooth surface, sharp edges and little or no warpage. The shaped products may be made in a variety of colors, and plastering may not be required on both sides of a wall built with sand lime shaped products. The process used to make sand lime shaped products may use siliceous wastes, thereby producing shaped products at less cost. The process may consume less energy than processes to make clay shaped products.
Sand lime shaped products may be prone to various problems associated with moisture or water absorption. For example, the shaped products may become dirty or stained due to the combination of moisture and dirt caused by rain or sprinklers, and the like. Mortar may begin to disintegrate between the shaped products, which can cause the part of the wall to collapse, or single shaped products to crumble or crack. Efflorescence results from shaped products getting wet, wherein salts from the shaped product dissolve in the water and are drawn out of the masonry as the moisture evaporates. Another problem is that once shaped products have become wet, the expansion of freezing water may break off the top surface of the shaped products, leaving the inner surface exposed. After a time, the shaped products may spall or crumble. Another problem is a dramatic increase of thermal conductivity of the soaked product, compared to the dry product due to heat conductivity of the water.
Many attempts have been made in the past to solve these problems, such as externally waterproofing the finished product. For example, U.S. Pat. No. 5,962,585 describes sealing a wall or a ceiling by brushing the external surfaces with a cream containing a silicone compound (e.g., C1–C20-alkyl-C2–C6-alkoxysilane).
However, using silicone or silicone-based water repellents externally on masonry products has the inherent disadvantages of high costs, additional coating labor costs, additional curing time and materials that are not friendly to the environment.
Other attempts have been made to solve these problems by incorporating a silicone oil water repellent additive during the sand lime production process. For example, U.S. Pat. No. 4,775,505 describes a process for preparing a water repellent calcium silicate shaped product, comprising dispersing a siliceous source and a calcareous source in water, mixing in a water repellent composition, reacting the mixture under heat to obtain an aqueous slurry that contains a calcium silicate hydrate, and pressfilter-molding the aqueous slurry, followed by drying or drying after steam-curing.
However, using silicone or silicone-based water repellents internally during production of masonry products has the inherent disadvantages of high costs, reduction of physical qualities of the product, and materials that are not friendly to the environment.
In addition, it is noted that the calcium silicate described in U.S. Pat. No. 4,775,505 is not a shaped product intended for bearing structural weights, such as sand lime bricks. Rather, as stated in the description, U.S. Pat. No. 4,775,505 “relates to a process for preparing a calcium silicate shaped product having a low bulk density and excellent flame and heat resistance, mechanical strength and dimensional stability and having uniform water-repellency throughout the interior of the product, which is thus suitable as a flame and heat resistant material, a heat insulator and a lagging material.” (Lagging material is thermal wrapping material used to thermally insulate pipes and ducting by wrapping therearound.) In other words, the calcium silicate product of U.S. Pat. No. 4,775,505 is formed into a very light weight product which may be used for thermal insulation purposes and the like (different from the present invention, which may be used for bricks, blocks, tiles, etc). The specific volume of the calcium silicate products in U.S. Pat. No. 4,775,505 is in the range of 15–23 cm3/g, which is a density range of 43.5–66.7 kg/m3 (different from the present invention with a density range of at least 200 kg/m3, preferably 1500 kg/m3).
It is further noted that U.S. Pat. No. 4,775,505 teaches diluting silicone-based water repellents with wax. However, U.S. Pat. No. 4,775,505 clearly states its inability to use wax as the water repellent additive (col. 5 lines 39–42): “the mixing ratio of the silicone oil and the paraffinic compound or low molecular weight hydrocarbon resin is preferably within a range of from 70:30 to 10:90 by weight ratio. Particularly preferred is a range of from 60:40 to 20:80. If the silicone oil is less than the above ratio, the water repellency will be inadequate, and if it exceeds the above ratio, the cost of the water repellent composition tends to be expensive, such being undesirable”.